1. Field of the Invention
This invention pertains to the control of upshifts and downshifts of an electronically-controlled automatic transmission. More particularly, the invention pertains to scheduling gear ratio changes on the basis of inferences drawn from current use of the vehicle engine and transmission.
2. Description of the Prior Art
Conventionally an electronically-controlled automatic transmission is provided with a gearshift schedule that defines when each gear ratio change is to occur on the basis of current engine throttle position and vehicle speed. Generally, data from lookup tables stored in electronic memory relating vehicle speed and engine throttle position, for each of the gear ratio changes, are used to produce a signal representing the desired gear ratio. When the desired gear ratio is different from the current gear ratio, a command signal is produced by the control to cause a change in state of solenoid-operated shift valves and a reduction of torque carried by an off-going friction element and an increase of torque carried by an on-coming friction element. This changes the state of the planetary gear units and cause the gear ratio to change.
Generally a reference schedule of gearshift boundaries, expressed in terms of vehicle speed and engine throttle position, is stored in memory. The schedule is continually referenced and used to produce an upshift signal or downshift signal when a boundry is crossed.
U.S. Pat. Nos. 4,669,335; 4,807,497; and 4,823,642 describe a switch used by the vehicle operator to signify preference for the transmission to be operated in economy mode or performance mode. The state of the mode switch is used as input information by a microprocessor so that decisions to change gear ratios are made with reference to a first standard gearshift schedule whose shift points are established for use in the economy mode and a second schedule for use in the performance mode. U.S. Pat. Nos. 4,338,666; 4,350,057; 4,474,081; 4,584,906; 4,679,145; and 4,733,580 disclose transmission control techniques wherein the gearshift schedule corresponding to either economy or performance mode of operation is automatically selected on the basis of vehicle operating parameters.
In certain driving conditions, when the engine throttle pedal is depressed quickly with the vehicle traveling at about 60 mph, the driver demands more power for fast acceleration. The gearshift schedule would be established to produce a downshift when the throttle position exceeds the throttle position that maintains 60 mph vehicle speed on a level road. However, in certain other vehicle operating situations, the vehicle may be required to cruise at various loads, especially at high loads above 60 mph. The gearshift schedule described above will produce frequent unwanted downshifts under those conditions.
To avoid this problem multiple gearshift schedules should be defined that satisfy driver demands for current driving condition. Use of a mode switch to change between specific shift schedules is one technique for providing increase flexibility to accommodate greatly different driver expectations and demands in use of the same vehicle.